In recent years, research has been done on a redirecting technology which can redirect rapidly a mobile terminal UE within communicating distance of a cell in which communication with a Universal Mobile Telecommunications System (UMTS) is available (hereinafter referred to as a UMTS cell) to a cell in which communication with a Long Term Evolution (LTE) system is available (hereinafter referred to as an LTE cell), in an overlapped area between the UMTS cell and the LTE cell. The LTE cell can provide higher-performance communications service (for example, Non Patent Literature 1).
FIG. 11 is a diagram showing an example of the redirecting technology. In FIG. 11, when the mobile terminal UE currently visited in the UMTS cell initiates communication in the overlapped area with the LTE cell, “RRC CONNECTION REQUEST” for requesting a Radio Resource Control (RRC) connection setup is transmitted to a radio control apparatus RNC of the UMTS system (Step S1001).
When an LTE supported identifier for indicating that the LTE system can be supported is included in the “RRC CONNECTION REQUEST” received from the mobile terminal UE, the radio control apparatus RNC determines that the mobile terminal UE should be redirected to the LTE cell, and transmits “RRC CONNECTION REJECT” for rejecting the RRC connection setup to the mobile terminal UE (Step S1002).
The mobile terminal UE is redirected to the LTE cell according to an instruction for being redirected to the LTE cell included in the “RRC CONNECTION REJECT” received from the radio control apparatus RNC, and the transmits “RRC CONNECTION REQUEST” to a wireless base station eNB of the LTE system (Step S1003). The mobile terminal UE sets up the RRC connection with the base transceiver stations eNB (Step S1004).